This relates to integrated circuits, and more particularly, to integrated circuits with storage elements that demonstrate soft error upset immunity.
Integrated circuits often contain volatile storage elements. Typical volatile storage elements may be based on cross-coupled inverters (latches). A volatile storage element retains data only so long as the integrated circuit is powered. In the event of power loss, the data in the volatile storage element is lost. Although nonvolatile storage elements such as memory elements based on electrically-erasable programmable read-only memory technology are not subject to data loss in this way, it is often not desirable or possible to fabricate nonvolatile storage elements as part of an integrated circuit.
As a result, volatile storage elements are often used. For example, a volatile storage element such as a flip-flop circuit includes a master latch and a slave latch, where each of the master and slave latches includes a pair of cross-coupled inverters. Such types of volatile storage elements are subject to a phenomenon known as soft error upset.
Soft error upset (SEU) events are caused by cosmic rays and radioactive impurities embedded in integrated circuits and their packages. Cosmic rays and radioactive impurities generate high-energy atomic particles such as neutrons and alpha particles. The storage elements contain transistors and other components that are formed from a patterned silicon substrate. When an atomic particle strikes the silicon in the storage element, electron-hole pairs are generated. The electron-hole pairs create a conduction path that can cause a charged node in the storage element to discharge and the state of the storage element to flip. If, for example, a “1” was stored in the storage element, a soft error upset event could cause the “1” to change to a “0.”
Upset events in an integrated circuit corrupt the data stored in the storage elements and can have serious repercussions on system performance. In certain system applications such as remote installations of telecommunications equipment, it is extremely burdensome to repair faulty equipment. Unless integrated circuits demonstrate good immunity to soft error upset events, they will be unsuitable for these types of applications.